This study examined treatment outcomes, including preserved fertility, menstrual regularity, and pregnancy outcomes, in patients with stage I epithelial ovarian cancer (EOC) or borderline ovarian tumors (BOTs) who underwent fertility-sparing surgery (FSS). Patients with stage I EOC and BOTs who were aged 18–45 years and underwent FSS between 2007 and 2022 were retrospectively reviewed. Significant differences between various subgroups in terms of disease recurrence, menstrual irregularity due to the disease, and pregnancy outcomes were analyzed. A total of 71 patients with BOTs and 33 patients with EOC were included. In the BOT group, the median age was 30 (range, 19–44) years. Recurrence occurred in eight patients, with one case exhibiting a malignant transformation into mucinous EOC. Among the 35 married patients with BOTs, 20 successfully conceived, resulting in 23 live births and 3 spontaneous abortions. A higher pregnancy rate was observed in those without prior childbirth (82.4%) than in those who had prior childbirth (33.3%). In the EOC group, the median age was 34 (range, 22–42) years. Recurrence occurred in one patient. Menstrual regularity was maintained in 69.7% of the patients. Among the 14 married patients in this group, 12 achieved a total of 15 pregnancies (including 2 twin pregnancies), 16 live births, and 1 spontaneous abortion. The results of the study confirmed that FSS is a favorable surgical option for young women with early-stage BOTs or EOC who wish to preserve their fertility. However, additional investigations are needed to validate these findings.